2-Stroke Engine Options for Automotive Use: A Fundamental Comparison of Different Potential Scavenging Arrangements for Medium-Duty Truck Applications 2019-01-0071
The work presented here seeks to compare several different means of providing scavenging systems for a 2-stroke engine suitable to power a US light-duty truck. It follows on from previous work investigating uniflow scavenging systems, and seeks to provide context for the results discovered there, as well as to assess the benefits of a new means of arranging the scavenging system for a 2-stroke engine which was invented as a result of that work: the reverse sleeve-valve uniflow process.
Five different scavenging systems were compared in detail. All were compared in terms of indicated fuel consumption for the same cylinder swept volume using a one-dimensional engine simulation package, and a new methodology for optimization was developed. The process also took into account charging system work.
As a result of this work it was found that the opposed-piston configuration provides the best attributes since it allows maximum expansion and minimum heat transfer. The other uniflow systems were next, with the reverse sleeve valve being the most promising. The loop-scavenged approach was found to compromised by its requirement to have intake and exhaust ports at the same height in the cylinder, thus lengthening the gas exchange events for any angle area, and reducing expansion and compression ratio. This was despite the use of a charge trapping valve to minimize charge short-circuiting.
Finally it was found that existing experiential guidelines for port angle-area specification for loop-scavenged, piston-ported engines using crankcase compression could also be applied to all of the other scavenging types, this being done in order to provide a starting point for the work. The optimizer also allowed further improvements to be made over the start point. The paper therefore presents a fundamental comparison of scavenging systems using a new approach, providing information which has not been shown before.
James W. G. Turner, Robert A. Head, Junseok Chang, Nayan Engineer, Roshan Wijetunge, David W. Blundell, Paul Burke
University of Bath, Saudi Aramco
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